The overall objective of this research program is an understanding of the neuroethological bases of auditory communication. To achieve this objective, behavioral experiments on processing of biologically-relevant vocal signals in a "simple" vertebrate auditory system will be conducted and the neurophysiological correlates of these phenomena will be examined. The major theme of the project is a quantitative analysis of temporal cues mediating recognition of species-specific communication sounds. An integrative neuroethological approach will be used to estimate absolute sensitivity and selectivity in noise to different kinds of temporal cues, particularly waveform periodicity and fine-temporal structure. Experiments will be conducted on 3 levels: (1) psychophysical; (2) ethological, studying the natural communication behavior; and (3) physiological. Because vocal communication in a noisy environment is a fundamental problem for many animals, the principles of neural coding derived from this research are relevant for understanding the representation of complex speech sounds in the human's nervous system. This research will also contribute to the understanding of the mechanism of pitch perception, a fundamental but difficult problem in psychoacoustics.